The goal of this project is to elucidate the mechanisms of electronic conductance in mesoscopic systems by studying experimentally their current fluctuations, or shot noise. The focus is on the determination of the noise when electrons tunnel through arrays of potential barriers created in a variety of semiconductor configurations, and on contrasting its value with existing theories of electronic conduction. Electron transport is induced, either electrically or optically, in GaAs-GaAlAs or Si-SiGe heterostructures at low temperatures (typically 4K or below), prepared by molecular beam epitaxy and sometimes patterned to sub-micrometer dimensions. This project addresses the following questions: Are the shot-noise characteristics of devices that exhibit negative differential conductance universal, that is, independent of the mechanism responsible for that negative conductance, as some theorists have suggested? Does quantum-mechanical coupling between (or among) quantum wells reduce noise as drastically as has been predicted? How large is the shot noise in strongly coupled superlattices, in which there is coherent transport? The answers illuminate basic concepts in mesoscopic conductors and probe the ultimate limits of devices. They have implications beyond the materials studied here, from organic materials to quantum dots and even to molecular electronics. The project trains graduate and undergraduate students to work together under the guidance of a senior scientist in an interdisciplinary topic, in which they probe deep physics questions; learn connections between science and technology; while being trained in a range of versatile materials-science techniques of permanent value for careers in industry, academia or government.
The random fluctuations of the electricity that flows through a conductor often give information that is veiled when only the average current is known. By better understanding how materials conduct electricity it becomes possible to determine the ultimate limits of today's devices and to design new ones with much improved characteristics. The goal of this project is to elucidate the mechanisms of electronic conductance in materials of fundamental and technological importance, by studying experimentally their current fluctuations, or electronic noise. The focus is on semiconductor heterostructures, which are widely used in applications and at the same time offer an almost ideal testbed for more complex materials of potential use in nanoelectronics, for instance plastics and carbon nanotubes. This project aims to answer questions such as: Are all devices that exhibit the same macroscopic behavior alike, or can we differentiate among them and select the optimum one for a specific application? or, How much smaller can devices become before they are limited by the "personality" of individual electrons? In looking for answers to these and similar questions, the project trains graduate and undergraduate students to work together under the guidance of a senior scientist in an interdisciplinary topic, in which they experience the connection between science and technology; while learning versatile materials-science techniques of permanent value for careers in industry, academia or government.
